The present invention relates to rotating element sheet material, a method of assembly of such rotating element sheet material, and a method of macroscopically addressing rotating element sheet material. More particularly, the present invention relates to rotating element sheet material that allows for the assignment of rotatable elements of specified classes to specified positions.
Rotating element sheet material has been disclosed in U.S. Pat. Nos. 4,126,854 and 4,143,103, both herein incorporated by reference, and generally comprises a substrate, an enabling fluid, and a class of rotatable elements. As discussed more below, rotating element sheet material has found a use as xe2x80x9creusable electric paper.xe2x80x9d FIG. 1 depicts an enlarged section of rotating element sheet material 18, including rotatable element 10, enabling fluid 12, cavity 14, and substrate 16. Observer 28 is also shown. Although FIG. 1 depicts a spherically shaped rotatable element and cavity, many other shapes will work and are consistent with the present invention. As disclosed in U.S. Pat. No. 5,389,945, herein incorporated by reference, the thickness of substrate 16 may be of the order of hundreds of microns, and the dimensions of rotatable element 10 and cavity 14 may be of the order of 10 to 100 microns.
In FIG. 1, substrate 16 is an elastomer material, such as silicone rubber, that accommodates both enabling fluid 12 and the class of rotatable elements within a cavity or cavities disposed throughout substrate 16. The cavity or cavities contain both enabling fluid 12 and the class of rotatable elements such that rotatable element 10 is in contact with enabling fluid 12 and at least one translational degree of freedom of rotatable element 10 is restricted. The contact between enabling fluid 12 and rotatable element 10 breaks a symmetry of rotatable element 10 and allows rotatable element 10 to be addressed. The state of broken symmetry of rotatable element 10, or addressing polarity, can be the establishment of an electric dipole about an axis of rotation. For example, it is well known that small particles in a dielectric liquid acquire an electrical charge that is related to the Zeta potential of the surface coating. Thus, an electric dipole can be established on a rotatable element in a dielectric liquid by the suitable choice of coatings applied to opposing surfaces of the rotatable element.
The use of rotating element sheet material 18 as xe2x80x9creusable electric paperxe2x80x9d is due to the fact that the rotatable elements are typically given a second broken symmetry, a multivalued aspect, correlated with the addressing polarity discussed above. That is, the above mentioned coatings may be chosen so as to respond to incident electromagnetic energy in distinguishable ways. Thus, the aspect of rotatable element 10 to observer 28 favorably situated can be controlled by an applied vector field.
For example, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, rotatable element 10 may comprise a black polyethylene generally spherical body with titanium oxide sputtered on one hemisphere, where the titanium oxide provides a light-colored aspect in one orientation. Such a rotatable element in a transparent dielectric liquid will exhibit the desired addressing polarity as well as the desired aspect.
Rotatable Elements with Two-valued Aspects
A multivalued aspect in its simplest form is a two-valued aspect. When the aspect is the chromatic response to visible light, rotatable element 10 with a two-valued aspect can be referred to as a bichromal rotatable element. Such a rotatable element is generally fabricated by the union of two layers of material as described in U.S. Pat. No. 5,262,098, herein incorporated by reference.
FIGS. 2-4 depict rotatable element 10 and an exemplary system that use such rotatable elements of the prior art. In FIG. 2, rotatable element 10 is composed of first layer 20 and second layer 22 and is, by way of example again, a generally spherical body. The surface of first layer 20 has first coating 91 at a first Zeta potential, and the surface of second layer 22 has second coating 93 at a second Zeta potential. First coating 91 and second coating 93 are chosen such that, when in contact with a dielectric fluid (not shown), first coating 91 has a net positive electric charge with respect to second coating 93. This is depicted in FIG. 2 by the xe2x80x9c+xe2x80x9d and xe2x80x9cxe2x88x92xe2x80x9d symbols respectively. Furthermore, the combination of first coating 91 and the surface of first layer 20 is non-white-colored, indicated in FIG. 2 by hatching, and the combination of second coating 93 and the surface of second layer 22 is white-colored. One skilled in the art will appreciate that the material associated with first layer 20 and first coating 91 may be the same. Likewise, the material associated with second layer 22 and second coating 93 may be the same.
FIG. 3 depicts no-field set 30. No-field set 30 is a subset of randomly oriented rotatable elements in the vicinity of vector field 24 when vector field 24 has zero magnitude. Vector field 24 is an electric field. No-field set 30, thus, contains rotatable elements with arbitrary orientations with respect to each other. Therefore, observer 28 in the case of no-field set 30 registers views of the combination of second coating 93 and the surface of second layer 22, and first coating 91 and the surface of first layer 20 in an unordered sequence. Infralayer 26 forms the backdrop of the aspect. Infralayer 26 can consist of any type of material or aspect source, including but not limited to other rotatable elements, or some material that presents a given aspect to observer 28.
FIG. 4 depicts first aspect set 32. First aspect set 32 is a subset of rotatable elements in the vicinity of vector field 24 when the magnitude of vector field 24 is nonzero and has the orientation indicated by arrow 25. In first aspect set 32, all of the rotatable elements orient themselves with respect to arrow 25 due to the electrostatic dipole present on each rotatable element 10. In contrast to no-field set 30, observer 28 in the case of first aspect set 32 registers a view of a set of rotatable elements ordered with the non-white-colored side up. Again, infralayer 26 forms the backdrop of the aspect. An alternate view of first aspect set 32 of FIG. 4 is depicted in FIG. 5. In FIG. 5, the symbol "THgr" indicates an arrow directed out of the plane of the figure. In FIGS. 4 and 5, rotatable element 10, under the influence of applied vector field 24, orients itself with respect to vector field 24 due to the electric charges present as a result of first coating 91 and second coating 93, as depicted in FIG. 2.
One skilled in the art will appreciate that first aspect set 32 will maintain its aspect after applied vector field 24 is removed, in part due to the energy associated with the attraction between rotatable element 10 and the substrate structure, as, for example, cavity walls (not shown). This energy contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 18, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, and discussed in more detail below.
Rotatable Elements with Multivalued Aspect
A rotatable element with multivalued aspect is generally fabricated as disclosed in U.S. Pat. No. 5,919,409, herein incorporated by reference. An exemplary rotatable element 10 with multivalued aspect is depicted in FIG. 6. Rotatable element 10 in FIG. 6 is composed of first layer 36, second layer 37 and third layer 38. The surface of third layer 38 has third coating 95 at a first Zeta potential, and the surface of first layer 36 has first coating 97 at a second Zeta potential such that third coating 95 has a net positive charge, xe2x80x9c+,xe2x80x9d with respect to first coating 97 when rotatable element 10 is in contact with a dielectric fluid (not shown). First layer 36, first coating 97, third layer 38, and third coating 95 can be chosen to be transparent to visible light and second layer 22 can be chosen to be opaque or transparent-colored to visible light, such that the rotatable element acts as a xe2x80x9clight-valve,xe2x80x9d as disclosed, for example, in U.S. Pat. No. 5,767,826, herein incorporated by reference, and in U.S. Pat. No. 5,737,115, herein incorporated by reference. As above, one skilled in the art will appreciate that the material associated with first layer 36 and first coating 97 may be the same. Likewise, the material associated with third layer 38 and third coating 95 may be the same.
Rotatable elements with multivalued aspect are generally utilized in rotating element sheet material that use canted vector fields for addressing. A canted vector field is a field whose orientation vector in the vicinity of a subset of rotatable elements can be set so as to point in any direction in three-dimensional space. U.S. Pat. No. 5,717,515, herein incorporated by reference, discloses the use of canted vector fields in order to address rotatable elements. The use of canted vector fields with rotating element sheet material 18 allows complete freedom in addressing the orientation of a subset of rotatable elements, where the rotatable elements have the addressing polarity discussed above.
One skilled in the art will appreciate that no-field set 30 and first aspect set 32 discussed above in FIGS. 3-5 can form the elements of a pixel, where vector field 24 can be manipulated on a pixel by pixel basis using an addressing scheme as discussed, for example, in U.S. Pat. No. 5,717,515, hereinabove incorporated by reference.
Work Function
As discussed above, a useful property of rotating element sheet material 18 is the ability to maintain a given aspect after the applied vector field 24 for addressing is removed. This ability contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 18, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference. This will be referred to as aspect stability. The mechanism for aspect stability in the above embodiments is generally the energy associated with the attraction between the rotatable elements and the substrate structure, or xe2x80x9cwork function.xe2x80x9d A host of factors influence the magnitude of the energy associated with the work function including, but not limited to: surface tension of enabling fluid in contact with first rotatable element or second rotatable element; the relative specific gravity of the rotatable elements to the enabling fluid; magnitude of charge on rotatable elements in contact with substrate structure, as, for example, cavity walls; relative electronic permittivity of enabling fluid and substrate structure; xe2x80x9cstickinessxe2x80x9d of substrate structure; and other residual fields that may be present. The applied vector field 24 for addressing must be strong enough to overcome the work function in order to cause an orientation change; furthermore, the work function must be strong enough to maintain this aspect in the absence of an applied vector field 24 for addressing.
FIG. 7 depicts an exemplary graph of number 54, N, of rotatable elements that change orientation as a function of applied vector field 24, V of the prior art. Work function 52, VW, corresponds to the magnitude of applied vector field 24 when the number 54 of rotatable elements that change orientation in response to vector field 24 has reached saturation level 56, NS, corresponding to the correlated orientation of all rotatable elements 10.
Microstructured Substrate
A desired property of rotatable element sheet material 18 is a high overall ratio of aspect area to surface area. With respect to chromatic aspects, this can be related to overall reflectance or transmittance. Reflectance of ordinary paper is approximately 85%. Reflectance of currently available electric paper is approximately 15% to 20%. U.S. Pat. No. 5,808,783, herein incorporated by reference, discloses a method of improving this value through the use of a dense monolayer of rotatable elements. Often, the arrangement of a dense monolayer is dependent upon the geometry of the substrate. Thus, it remains desirable to fabricate substrate 16 such that it can accommodate a dense monolayer of rotatable elements.
A further desired property of rotating element sheet material is the placement of rotatable elements of different classes to precise positions within the substrate, such that the rotatable elements of given classes are in a regular, repeating pattern in a substantially single layer, and such that the regular, repeating pattern is correlated with an addressing array. In this way, rotatable elements of a given class are located proximal to the corresponding addressing element of the given class. For example, it is desirable in a cyan-magenta-yellow color scheme, where each pixel of an aspect viewing area contains an addressing element for, respectively, cyan, magenta, and yellow, to place all rotatable elements with a cyan-colored aspect proximal to the cyan addressing element, all rotatable elements with a magenta-colored aspect proximal to the magenta addressing element, and all rotatable elements with a yellow-colored aspect proximal to the yellow addressing element.
A further desired property of rotating element sheet material 18 is the ability to present several aspects of rotating element sheet material 18 with a relatively simple addressing scheme. Of particular interest are macroscopically viewed aspects, or multi-message aspects.
Accordingly, a first embodiment of the present invention of rotating element sheet material comprises a substrate, a plurality of rotatable elements of a first class, and a plurality of rotatable elements of a second class, where the substrate comprises a cavity-containing matrix having a plurality of cavities of a first class and a plurality of cavities of a second class. The plurality of rotatable elements of a first class are disposed within the plurality of cavities of a first class, and the plurality of rotatable elements of a second class are disposed within the plurality of cavities of a second class. Furthermore, the plurality of cavities of a first class and the plurality of cavities of a second class are arranged in a regular, repeating pattern in a substantially single layer. By addressing the plurality of cavities of a first class with a first addressing vector field, and addressing the plurality of cavities of a second class with a second addressing vector field, a display with multivalued aspects may be conveniently created.
A second embodiment of the present invention of rotating element sheet material comprises a substrate, a plurality of rotatable elements of a first class, and a plurality of rotatable elements of a second class, where the substrate comprises a cavity-containing matrix having a plurality of cavities of a first class and a plurality of cavities of a second class. The plurality of rotatable elements of a first class are disposed within the plurality of cavities of a first class, and the plurality of rotatable elements of a second class are disposed within the plurality of cavities of a second class. The plurality of rotatable elements of a first class have a common first addressing polarity and a common first work function. The plurality of rotatable elements of a second class have a common second addressing polarity and a common second work function. Furthermore, the common first work function is less than the common second work function. The plurality of cavities of a first class and the plurality of cavities of a second class are arranged in a substantially single layer and are arranged in a pattern that can be decomposed into a set of first aspect areas, a set of second aspect areas, and a set of null aspect areas. A macroscopic region that undergoes a correlated change in orientation of a set of rotatable elements in response to a change in the magnitude of the applied vector field determines an aspect area. Thus, a first aspect area is that macroscopic region that undergoes a correlated change in orientation of rotatable elements of a first class in response to a change in the applied vector field from essentially a zero value to the first work function, and that undergoes a correlated change in orientation of rotatable elements of a second class in response to a change in the applied vector field from the first work function to the second work function. Furthermore, a second aspect area is that macroscopic region that undergoes a correlated change in orientation of rotatable elements of a second class in response to a change in the applied vector field from essentially a zero value to the second work function, where the second work function is greater in magnitude than the first. The null aspect areas are those portions of the substrate that do not contain rotatable elements of a first class or rotatable elements of a second class or that contain rotatable elements that do not change orientation under the applied vector field. By addressing a macroscopic region with an addressing vector field that may be changed to selectively change one or more aspect areas, a multi-message display may be conveniently created.
In an embodiment of a method for assembling either the first embodiment of rotating element sheet material or a second embodiment of rotating element sheet material, the method comprises: providing a substrate component defining a plurality of microrecesses of a first class and a plurality of microrecesses of a second class; dispersing a plurality of rotatable elements of a second class onto the substrate component, where the rotatable elements of a second class are configured to preferably settle into the plurality of microrecesses of a second class only; and then dispersing a plurality of rotatable elements of a first class, where the rotatable elements of a first class are configured to settle into either the plurality of microrecesses of a first class or the plurality of microrecesses of a second class, but that the plurality of rotatable elements of a first class settle into the plurality of microrecesses of a first class only, since the plurality of microrecesses of a second class are already populated by the rotatable elements of a second class. The rotating element sheet material is then finished by the application of a substrate cover and enabling fluid.
In an embodiment of a method of macroscopically addressing the second embodiment of rotating element sheet material, the method comprises: providing the second embodiment of rotating element sheet material; introducing the second embodiment of rotating element sheet material to a macroscopic vector field at a first magnitude, where the first magnitude is greater that the first work function and less than the second work function; and then changing the magnitude of the macroscopic vector field from the first magnitude to a second magnitude, where the second magnitude is greater than the second work function. The effect of such a method of macroscopic addressing is to produce a dynamic change in a macroscopically viewed aspect of the rotating element sheet material, where the change in the macroscopically viewed aspect is determine by the first aspect areas, the second aspect areas, and the null aspect areas of the second embodiment of rotating element sheet material.